1. Field of the Invention
The invention relates to a position control device of the type riding over a surface for remotely controlling, say, movement of a cursor over a visual display, or for X-Y measuring purposes--i.e., it relates to a "mouse", as commonly termed in computer art.
2. Prior Art
Devices of this type are well-known (see, for example, my pending application Ser. No. 572,233 filed Jan. 19, 1984 and entitled "Remote Cursor Positioning Apparatus", and U.S. Pat. Nos. 3,269,190; 3,541,541; 3,835,464; 3,892,963 and 3,987,685). In general such devices have utilized pairs of transducer members, each member affixed to a shaft lying axially parallel to the generally flat surface upon which the X-Y position device is moved, each shaft either being attached directly to a wheel contacting the surface and rotating in a plane perpendicular to the surface on which movement is being generated, or else the shaft being supported such that it can be driven by frictional contact with what is termed a "transport sphere" or "transport wheel". Tilting of the wheel type of transport is known from the above-mentioned U.S. Pat. No. 3,892,963 but there the transducer shaft remained axially parallel to the contact surface--i.e., horizontal.
The first arrangement (direct connection) has the advantage of simplicity of structure, involving fewer parts as compared to the transport-driven shaft. In both arrangements, however, the size of the transducer member (a drum or disk, for example, with known indicia for detecting movement) has been limited both by the size of the wheel and by the need for clearance relative to housing surfaces. Therefore the transducer member has been of significantly smaller diameter than the wheel, the ratio of circumferential movement of the transducer drum or disk per unit of incremental movement of the wheel being much less than unity as a result. Under these conditions, the required fineness of the spacing between the movement indicia on the transducer member has been such that a very high order of accuracy is necessary if one attempts to increase the number of output signals from the transducer per unit of wheel movement.
On the other hand, consider position controllers of the type utilizing transport elements--e.g., a sphere (U.S. Pat. No. 3,987,685) or respective tilted transport wheels (U.S. Pat. No. 3,892,963)--for frictional driving of two orthogonally-oriented horizontal shafts bearing the respective X-Y transducers. Such transport elements tend to be relatively large and massive, thus having a higher moment of inertia than desirable--resulting in potential for error, particularly when there is a sudden initiation of motion of complete reversal in direction. Further, controllers of this type suffer the defect that they tend to slip when the support surface is very smooth or has a superficial film of oil or other lubricious fluid, this film being picked up and transferred to the contact area between transport element and shaft, causing more slip with resultant loss of accuracy. Another defect of some of this prior art is that transport spheres are "free" and require capture members to retain them in the housing. These members must readily release the spheres so they can be cleaned periodically in order to remove the above-mentioned films and dirt accumulations. Alternatively, known devices for automatic continuous cleaning must be incorporated, necessitating undue complexity in either case.
Lastly, the foregoing devices tend to be susceptible to damage from severe shock caused by carelessness of use or by the tendency of the user to vent his frustration on the inanimate object at hand--namely the X-Y position controller or "mouse".